1. Field of the Invention
The present invention relates to a writing instrument including a stick-shaped material propelling mechanism.
2. Description of the Related Art
Conventionally, as this kind of writing instrument, for example, the ones described in Japanese Utility Model Publication No. 5-45513 and in Japanese Patent Laid-Open No. 4-25499 are known.
In a propelling pencil described In Japanese Utility model Publication No. 5-45513, a writing shaft body is disposed in an outer barrel, a spiral groove is provided in an inner surface of a rear part of a cylindrical cap, and a rear portion of a cylindrical body is attached to the cylindrical cap so as to be relatively rotatable, a slit is provided at a rear portion of the cylindrical body, an eraser bearer is slidably fitted into the slit, a projection provided at the eraser bearer is screwed into the spiral groove, and a front portion of the cylindrical body is attachable and detachable to and from the outer barrel, relatively unrotatable and movable in an axial direction.
In the propelling pencil described in Japanese Patent Laid-Open No. 4-25499, a writing body is disposed in an outer barrel, a projection is formed on an inner peripheral surface of a rear end of a lead tank of the writing body, a long groove which is engaged with the projection and a threaded groove are formed on a holder as an eraser bearing, a thread projection mated with the threaded groove of the holder is formed on an inner peripheral surface of a rotary sleeve, and the rotary sleeve is mounted on a rear end portion of the lead tank so as to be relatively rotatable.
In each of the above documents, the eraser held by the eraser bearer is capable of projecting and retracting from the rear end of the rear barrel by relative rotation between the outer barrel and the rear barrel.
However, in the former document, the number of components is large, and in both the documents, the eraser bearer and the rear barrel are screwed in each other, and the eraser held in the eraser bearer is propelled while relatively rotating with respect to the rear barrel, and therefore, there arises the problem that a distance along which the eraser slides in contact with the inner peripheral surface of the rear barrel is long with respect to the propelling amount of the eraser, and therefore, the operation efficiency is low.